import java.util.Scanner;
public class Main {
	public static void main(String args[]){
		Scanner sc=new Scanner(System.in);
		int n=Integer.parseInt(sc.nextLine()),begin,end,sum=0;
		String s[];
		int are[]=new int[4];
		for(int i=0;i<n;i++){
			s=sc.nextLine().split(" |:");
			for(int j=0;j<4;j++)
				are[j]=Integer.parseInt(s[j]);
			if(are[0]>are[2] || (are[0]==are[2] && are[1]>are[3]))
				are[2]+=24;
			begin=are[0]*60+are[1];
			end=are[2]*60+are[3];
			sum+=(end-begin);
		}
		System.out.println(sum);
	}
}